Currently, excess heat flow from a steam seal header is dumped to a condenser as illustrated in FIG. 1. This steam can be at a very high temperature—up to 900° F. depending on the throttle and reheat temperature of the unit. This excess heat could be used to produce power by admitting into downstream low pressure stages. However, due to the high, perhaps even excessive mismatch between the dump steam and the low pressure reentry stage temperature, there are many unfavorable mechanical implications.
Hence, before admitting the dump steam into the low pressure stage, the temperature of the dump steam needs to be brought down within acceptable limits. Conventionally, this is achieved through attemperation, mixing with low grade steam, and so on. But such conventional methods can be wasteful in that the heat of the dump steam lost through attemperation is not used for useful work. This reduces the steam turbine cycle efficiency. Also the heat transfer is limited by the sink temperature of the heat exchanger (in the case of feed water heater line). The dump steam cannot be cooled below the feed water heat temperature conventionally without using attemperation.
It would be desirable to utilize the excess heat, and thereby enhance the efficiency of the steam turbine cycle.